The present invention relates to an image sensing or reading apparatus for converting optical image information into electrical, signals, and more specifically relates to an image line sensor of the integrated type having a plurality of opto-electro conversion elements aligned linearly in a row.
Recently, image reading apparatuses have been widely used in facsimiles and word processors for reading and inputting characters and figures as image data. Conventionally, these apparatuses are comprised of a plurality of opto-electro conversion elements for converting image information into electrical signals, corresponding switching elements and a scanning circuit for sequentially reading the image electrical signals obtained by the opto-electro conversion elements, and a control circuit for controlling the switching elements and scanning circuit.
FIG. 3 is a timing chart showing the operation of a conventional image reading apparatus of the line scanning type. The scanning circuit receives an initiating signal SI effective to initiate each line scanning of the linearly arranged opto-electro conversion elements through the corresponding switching elements and outputs an ending signal SO indicative of the ending of each line scanning when the n-th opto electro conversion element of the last stage is accessed to read out the corresponding n-th electrical signal SIG. The scanning circuit is responsive to clock pulses CK to sequentially scan the n number of conversion elements. The scanning circuit is comprised of n number of flipflops, and the last stage flipflop produces an output pulse, which is directly used as the ending signal SO so that the ending signal SO coincides with the last n-th electrical signal SIG.
Accordingly, in the above described conventional image reading apparatus, the last bit electrical signal SIG produced by the last stage conversion element includes switching noise due to the ending signal SO. Therefore, the signal to noise ratio (S/N ratio) is reduced which is an obvious drawback.